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<a name="Further-Interoperability-of-Fortran-with-C-1"></a>
<h4 class="subsection">7.1.6 Further Interoperability of Fortran with C</h4>

<p>The Technical Specification ISO/IEC TS 29113:2012 on further
interoperability of Fortran with C extends the interoperability support
of Fortran 2003 and Fortran 2008. Besides removing some restrictions
and constraints, it adds assumed-type (<code>TYPE(*)</code>) and assumed-rank
(<code>dimension</code>) variables and allows for interoperability of
assumed-shape, assumed-rank and deferred-shape arrays, including
allocatables and pointers.
</p>
<p>Note: Currently, GNU Fortran does not support the array descriptor
(dope vector) as specified in the Technical Specification, but uses
an array descriptor with different fields. The Chasm Language
Interoperability Tools, <a href="http://chasm-interop.sourceforge.net/">http://chasm-interop.sourceforge.net/</a>,
provide an interface to GNU Fortran&rsquo;s array descriptor.
</p>
<p>The Technical Specification adds the following new features, which
are supported by GNU Fortran:
</p>
<ul>
<li> The <code>ASYNCHRONOUS</code> attribute has been clarified and
extended to allow its use with asynchronous communication in
user-provided libraries such as in implementations of the
Message Passing Interface specification.

</li><li> Many constraints have been relaxed, in particular for
the <code>C_LOC</code> and <code>C_F_POINTER</code> intrinsics.

</li><li> The <code>OPTIONAL</code> attribute is now allowed for dummy
arguments; an absent argument matches a <code>NULL</code> pointer.

</li><li> Assumed types (<code>TYPE(*)</code>) have been added, which may
only be used for dummy arguments.  They are unlimited polymorphic
but contrary to <code>CLASS(*)</code> they do not contain any type
information, similar to C&rsquo;s <code>void *</code> pointers.  Expressions
of any type and kind can be passed; thus, it can be used as
replacement for <code>TYPE(C_PTR)</code>, avoiding the use of
<code>C_LOC</code> in the caller.

<p>Note, however, that <code>TYPE(*)</code> only accepts scalar arguments,
unless the <code>DIMENSION</code> is explicitly specified.  As
<code>DIMENSION(*)</code> only supports array (including array elements) but
no scalars, it is not a full replacement for <code>C_LOC</code>.  On the
other hand, assumed-type assumed-rank dummy arguments
(<code>TYPE(*), DIMENSION(..)</code>) allow for both scalars and arrays, but
require special code on the callee side to handle the array descriptor.
</p>
</li><li> Assumed-rank arrays (<code>DIMENSION(..)</code>) as dummy argument
allow that scalars and arrays of any rank can be passed as actual
argument. As the Technical Specification does not provide for direct
means to operate with them, they have to be used either from the C side
or be converted using <code>C_LOC</code> and <code>C_F_POINTER</code> to scalars
or arrays of a specific rank. The rank can be determined using the
<code>RANK</code> intrinisic.
</li></ul>


<p>Currently unimplemented:
</p>
<ul>
<li> GNU Fortran always uses an array descriptor, which does not
match the one of the Technical Specification. The
<code>ISO_Fortran_binding.h</code> header file and the C functions it
specifies are not available.

</li><li> Using assumed-shape, assumed-rank and deferred-shape arrays in
<code>BIND(C)</code> procedures is not fully supported. In particular,
C interoperable strings of other length than one are not supported
as this requires the new array descriptor.
</li></ul>


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